Lecture 4 Flashcards
What are the 5 Ls of lifting and describe them
- Load: the amount of weight moved
- leverage: you want mechanical advantage - usually easier to lift if you bring the load closer to your COG and BOS
- Lungs: never hold your breath when exerting - lawyers exhale
- legs: use your legs not your back - lowering your COG by bending the lower extremities while maintaining a comfortable position with your back
lordosis: protect your back by maintaining a balanced neutral spine
what is inertia
the resistance an object (body) has to a change in state of motion
-the inertia of an object (body) is directly proportional to its mass
Torque
a rotational force
will cause an angular acceleration of a body around an axis
Torque equation
T=F (force) x Distance (moment arm)
What is Newton’s first law of inertia
-linear: a body remains at rest or at a constance linear velocity except when compelled by an external force to change its state
rotational: a body remains at rest or at a constant angular velocity around an axis of rotation unless compelled by an external torque to change its state
Newtons second law of acceleration
linear: linear acceleration of a body is directly proportional to the force causing it, takes place in the same direction in which the force acts and is inversely proportional to the mass of the body
Rotational: the angular acceleration of a body is directly proportional to the torque causing it, takes place in the same rotary direction in which the torque acts and is inversely proportional to the mass moment of inertia
Radius of gyration
average distance between the axis of rotation and center of mass of a body or segment
-the larger the radius of gyration, the more mass moment of inertia there is (mass further from the axis) therefore the rotation is slower
what is mass moment of inertia with the equation
resistance to a change in angular velocity
-depends on mass of object or segment and is distribution with respect to axis of rotation
-I=mxr2
Newtons law of action-reaction
linear: for every force there is an equal and opposite directed force
Rotational: for every torque there is can equal and opposite directed torque
mechanical advantage equation
MA = EA/RA
(>1 means effort can overcome resistance without expending as much force as resistance)
effort force
muscle force or internal force
resistance force
external force
First class lever
EF axis RF
-MA depends on magnitude of forces and points of application
Second class levers
Axis RF EF (wheelbarrow)
Third class levers
EF between axis and RF
-MOST COMMON
-MA always <1
-RF always has MA
